Generally, a magnetic recording medium is manufactured in such a manner that a magnetic paint, which is prepared by uniformly dispersing a ferromagnetic powder, an abrasive, an antistatic agent such as carbon black, a lubricant, a hardener, and other additives, in a macromolecular resin material that is so-called a binder to which a solvent may suitably be added, if required, such magnetic paint is coated over a support, and dried up.
Heretofore, there has been a known magnetic recording medium comprising carbon black added in its magnetic layer containing ferromagnetic metal powder or tabular-shaped particulate magnetic material of barium-ferrite, Ba-Fe, so as to improve the abrasion resistance of the magnetic layer and to reduce the specific surface resistance.
When a magnetic recording medium contains carbon black in its magnetic layer, there is a defect that the electromagnetic conversion characteristics of the recording medium are deteriorated by worsening the surface roughness of the magnetic layer and lowering the packing density of the magnetic material.
Particularly with carbon black which is excellent in abrasion resistance and has an average particle size of not smaller than 50 m.mu., the surface roughness of the magnetic layer is made greater, so that the chroma S/N of a magnetic recording medium is lowered.
On the other hand, carbon black having an average particle size of not larger than 50 m.mu. and an oil absorption of not less than 100 ml, which is used for reducing the specific surface resistance of a magnetic layer, is so hard to disperse in the magnetic layer, so that the orientation and packing density of the magnetic material are deteriorated to result in the lowering of the chroma output of the magnetic recording medium.
There is another known technique in which a magnetic layer which has a layer-thickness of not thinner than 4.0 .mu.m and contains ferromagnetic metal powder or magnetic barium-ferrite particles is coated on a dried subbing layer containing carbon black.
When the layer thickness of the magnetic layer that is the upper layer is not thinner than 4.0 .mu.m, the effect of the carbon black-containing lower layer is lost, so that the drop-out of a magnetic recording medium is increased, because the specific surface resistance of the magnetic layer is not lowered, but remains as high as dust is apt to be attracted.
The above-described technique uses the so-called wet-on-dry multilayer-coating system that is to multilayer-coat a magnetic paint over a dried lower layer. In the technique, therefore, not only the processing steps are complicated, but also the surface roughness of the subbing layer affects its magnetic layer, so that the chroma S/N of the magnetic recording medium is lowered.